Loading of old worlds is temporarily disabled

Hi,

Hope someone here can help!

For about 2 weeks now I have not been able to load my old worlds as an error message comes up next to the world name titled: "Loading of old worlds is temporarily disabled" - I have ignored the issue and just selected 'New World' as I thought the issue would resolve itself but the message is still the same. My PC automatically downloads Java Minecraft updates (currently  version 21w07a) so I am not sure what is going on here, any ideas or should I just wait longer for this to resolve itself?

Many thanks